1. Field of the Invention
This invention relates generally to a video signal processing apparatus and more particularly, the invention relates to a video signal processing apparatus for reproducing luminance and color difference signals from a video signal including a time-compressed luminance and color difference signals in one horizontal scanning line interval, their time-compressed factors being different each other.
2. Description of the Prior Art
A video signal processing apparatus is used for reproducing luminance and color difference signals from a time-division-multiplexed video signal including a time-compressed luminance and color difference signals by time-expansion. Such a video signal is employed in MAC (Multiplexed Analog Components), TCI (Time Compressed Insertion) systems, and other systems using time-division-multiplexed video signal.
FIG. 3 shows an MAC system video signal. In FIG. 3, block 1 includes synchronizing and data signals; block 2, a color difference signal which is time-compressed by 1/3; and block 3, a luminance signal which is time-compressed by 2/3. These signals are transmitted for 1 H (one horizontal scanning interval). FIG. 4 shows a TCI system video signal. In FIG. 4, block 21 includes synchronizing and data signals: block 22, a color difference signal which is time-compressed by 1/4; and block 23, a luminance signal which is time-compressed by 1. These signals are transmitted for 1 H.
A prior art video processing circuit is shown in FIG. 9 of a block diagram. In FIG 9, an input video signal "a" is applied to an input terminal 11 and is sent to a time-expansion circuit 12, a time-expansion circuit 14, and a signal generation circuit 17. The time-expansion circuit 12 expands a luminance signal of the video signal "a" by an expansion ratio of three to reproduce a luminance signal with respect to time base. The time-expansion circuit 14 expands a color difference signal of the video signal "a" by an expansion ratio of 3/2 to reproduce a color difference signal with respect to time base. Time-expanded signals "b" and "d" are sent to an inverse matrix circuit 10 through a line memory 13 and a color difference signal reproduction circuit 15 respectively. The line memory 13 adjusts timing relation between these video signals. The color difference signal reproduction circuit 15 reproduces simultaneously two color difference signals from two successive horizontal scanning lines of the signal "d". The inverse matrix circuit 16 produces primary color signals R. G. and B sent to a display 18. The time-expansion circuits 12 and 14 are controlled by clocks from a signal generating circuit 17 which generates clock signals by an unshown phase-locked loop circuit responsive to a horizontal synchronizing pulse detected from the input video signal.
As mentioned above, the prior art video processing apparatus reproduces a video signal from time-compressed video signals. However, there is a drawback that when an output signal of the phase-locked loop circuit (PLL) of the signal generation circuit 17 is out of phase with its input signal, i.e. not locked, the time-expanded luminance signal becomes out of phase with the time-expanded color difference signal because time expansion ratios of the time-expansion circuits 12 and 14 are different therebetween. Therefore, there are two types of disturbed images, i.e., color and luminance images on the display 18 when the PLL is not locked. Such a disturbed color image over the disturbed luminance image gives a viewer unpleasant feeling. In other words, a reproduced video image on the display 18 has a double image of luminance and color images when the PLL is not locked.